An image forming apparatus that employs a belt unit having an endless belt and multiple belt supporting members support and circulate the endless belt in a loop is known, as disclosed in Japanese Patent Application Publication No. 2003-216001 (JP-2003-216001-A). Specifically, the image forming apparatus of JP-2003-216001-A includes four photoconductors that respectively form toner images of yellow, magenta, cyan, and black component colors. The image forming apparatus of JP-2003-216001-A also includes a belt-type transfer unit that transfers these toner images and forms a full-color toner image by superimposing these yellow, magenta, cyan, and black toner images from the four photoconductors onto a surface of an endless intermediate transfer belt provided in the transfer unit using a known electrophotographic process. The transfer unit can switch the degree of tension on the endless intermediate transfer belt at least between a taut use state for actual image formation and loose detachment state. The use state enables the intermediate transfer belt to circulate while remaining in contact with one or more photoconductors to form an image. The detachment state enables the intermediate transfer belt to be separated from all four of the photoconductors to allow a user to pull the transfer unit out of the image forming apparatus.
More specifically, primary transfer rollers for yellow, magenta, cyan, and black are supported by a frame unit to sandwich the intermediate transfer belt and form transfer nips thereon with the yellow, magenta, cyan, and black photoconductors, respectively. Then, by moving the frame unit, accordingly the yellow, magenta, cyan, and black primary transfer rollers, the intermediate transfer belt previously contacting the yellow, magenta, cyan, and black photoconductors separates therefrom. The transfer unit can then be readily pulled out, thereby facilitating maintenance thereof.
However, in such an image forming apparatus, ease of maintenance of the primary transfer rollers on the transfer unit pulled out from the housing has been almost neglected. That is, in general, to maintain the yellow, magenta, cyan, and black primary transfer rollers arranged within the loop of the endless intermediate transfer belt, these rollers need to be detached and removed from the loop thereof. Thus, an operator needs to insert his or her hand into an opening formed in both lateral sides of the intermediate transfer belt. However, such an opening is generally covered by a side plate which supports the multiple belt support rollers at both longitudinal ends. With such a configuration, since insertion of the hand into the belt loop is difficult and the primary transfer rollers are hardly visible within the belt loop, as a practical matter the primary rollers cannot be detached in such a state. Accordingly, the intermediate transfer belt is generally detached from the transfer unit prior to detachment of the primary rollers to provide ready access thereto, requiring extraordinary time and effort.
Even in such a situation, the system described below can be employed to solve such a problem. That is, four rollers supporting the intermediate transfer belt are independently movably disposed in the vicinity of the primary transfer rollers for yellow, magenta, cyan, and black component in the transfer unit, respectively. Typically, when a yellow primary transfer roller is to be maintained, for example, the operator executes the following operations. Initially, he or she pulls the transfer unit out from the housing. Then, he or she reduces the tension of the intermediate transfer belt on the transfer unit by sliding tension roller or the like, for example. Subsequently, he or she displaces one of the four belt rollers arranged in the vicinity of the yellow transfer roller from the inside to the outside of the belt loop so that the opening of the belt is pushed up to be exposed from the side plate in the vicinity of the yellow transfer roller. Hence, he or she can at last access the yellow transfer roller via the opening of the belt now pushed up in this way. The same goes for each of the remaining component transfer rollers. Accordingly, the primary transfer rollers of the respective colors can to some extent be maintained, although such a configuration employing dedicated rollers increases cost.